The present invention relates to a process for upgrading heavy crude and, more particularly, for upgrading heavy crude having high contents of asphaltenes and metals so as to increase the yield of distillates.
Ever increasing energy demands in combination with decreasing reserves of light crudes and the existence of large deposits of heavy crudes have made it highly desirable to develop new processes for upgrading heavy crudes into more valuable hydrocarbon products. While various prior art processes claim to effectively convert heavy crudes to lighter crudes, none have proved to be commercially viable for various reasons. For example, visbreaking has been found to be an effective method for increasing the yield of gasoline at the expense of the residual fractions, but visbreaking by itself is not sufficient for obtaining high yields of distillable products, and moreover there is the serious disadvantage that increasing severity to reach greater yields results in more unstable products and increased production of coke.
U.S. Pat. Nos. 4,179,355, 2,717,285, 3,132,088, and 3,148,135 disclose combinations of processes such as visbreaking, deasphalting and hydrogenation, which also does not guarantee economically obtaining high yields of liquids at the expense of the asphaltenes and resins.
The process described in European Pat. No. 0048098 A2 consists of a less severe visbreaking in the presence of fine particulate solids of coal, which permits reaching greater yields of distilled products, but at the expense of a segregation and deposition of coke on the solid particles; the visbreaking effluents then pass to a deasphalting unit to separate the asphalt solids, with later separation in aqueous medium of the solid organic phase (in suspension) of the inorganic ash, which stay sedimented.
British Pat. No. 2,074,186 A consists of a deasphalting of the charge, followed by a hydrovisbreaking of the deasphalted oil (DAO), and finally a stage of conversion in the presence of a catalyst.
Other patents, such as U.S. Pat. Nos. 3,280,073 and 3,293,169 also claim a thermal process followed by a catalytic hydrocracking including a previous deasphalting.
As can be seen, none of the processes mentioned obtain a greater yield of liquids by means of a controlled conversion of asphaltenes.
There exist in the prior art, processes which utilize a hydrogen donor in the hydroconversion stage, as disclosed in U.S. Pat. No. 3,338,818. This permits a greater severity to be reached in the hydroconversion stage without greater formation of coke, with an appreciable conversion of asphaltenes and a conversion of the 950.degree. F. fraction amounting to 50 vol. %. However, the use of a hydrogen donor requires the introduction into the overall scheme of the process an additional hydrogenation stage, which has the result of a different product distribution from that obtained by means of the present invention, at a high cost.
Accordingly, it is the principal object of the present invention to provide a process for the controlled conversion of asphaltenes and resins and a high conversion of the residual fraction.
It is a particular object of the present invention to provide a process for the controlled conversion of asphaltene resins which is relatively inexpensive to practice.
Further objects and advantages will appear hereinbelow.